Aryna Sabalenka launched the defence of her US Open crown with victory Sunday while Novak Djokovic made a successful start to his latest bid for a record 25th Grand Slam singles title — but a raging Daniil Medvedev exited.

World number one Sabalenka, bidding to become the first woman to claim back-to-back US Open titles since Serena Williams completed a hat-trick of wins in 2014, was made to work hard en route to a 7-5, 6-1 victory over Switzerland’s Rebeka Masarova.

Masarova, ranked 108th in the world, pushed Sabalenka out of her comfort zone with a gutsy performance on the Billie Jean King National Tennis Center’s main Arthur Ashe Stadium showcourt.

“Happy to get this win and happy to be in the second round. I feel like I didn’t start my best in the first games, but then I found my rh

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